code: def step(self, action):
      if action == 0:
          pass
      elif action == 1:
          self.n *= 2
      elif action == 2:
          self.n /= 2
      else:
          raise RuntimeError("bad action")
      obs = {"n": self.n}
      done = self.n.sum() < 1
      reward = abs(self.n.sum() - 4)
      return obs, reward, done
  
file_path: moolib/test/unit/test_envpool.py
imports: import random
  import pytest
  import torch
  import moolib
label_desc: Use image node_id 2 for calling the Env obj's underlying member method code with example usage: obj.step(action) and returns: obs,  reward,  done